Technical Field
[0001] The present invention relates to a composite material comprising resin and a graphene-like
carbon material such as graphene or lamina graphite, and more specifically to a composite
material in which a graphene-like carbon material has a higher adhesion to a substrate
composed of resin, and a method for producing the same.
Background Art
[0002] In the past, carbon materials such as graphite, carbon nanotube, carbon fiber and
carbon particles have been widely used as a reinforcing agent or a filler for resin.
Also, lamina graphite with a smaller number of graphene layers, which is prepared
by the exfoliation of graphite, has been recently attracting attention.
[0003] As a composite material of carbon materials and resin described above, a composite
material prepared by dispersing a carbon material such as carbon fiber in an epoxy
resin is known as described in the following Patent Literature 1.
Citation List
Patent Literature
[0004] Patent Literature 1: Japanese Patent Laid-Open No.
2003-277471
Summary of Invention
Technical Problem
[0005] However, conventional composite materials of resin and carbon materials had a problem
of poor adhesion strength between resin and carbon materials. For example, although
physical properties of a composite material prepared by dispersing a carbon material
in resin were improved by the addition of the carbon material as described in Patent
Literature 1, the adhesion strength to the carbon material was insufficient.
[0006] An object of the present invention is to solve the above defect of the conventional
art and provide a composite material having excellent adhesion between resin and a
graphene-like carbon material, and a method for producing the same.
Solution to Problem
[0007] The composite material according to the present invention comprises a substrate composed
of resin and a graphene-like carbon material layer provided so as to cover at least
part of the surface of the substrate, wherein graphene-like carbon is closely attached
to the surface of the substrate.
[0008] In a particular aspect of the composite material according to the present invention,
some of the graphene-like carbon penetrates the substrate from the surface of the
substrate toward the inner part. As a result, the adhesion between the two is further
improved.
[0009] In another particular aspect of the composite material according to the present invention,
the substrate composed of resin is of fine resin particles and the graphene-like carbon
material layer is formed so as to cover the outer surface of the fine resin particles.
In this aspect, since the outer surface of the fine resin particles is covered with
the graphene-like carbon material layer and some of the graphene-like carbon penetrates
the surface of the fine resin particles, the adhesion between the fine resin particles
and the graphene-like carbon material layer is improved. Furthermore, the composite
material in the form of fine particles which has a graphene-like carbon material layer
on the surface is less likely to coagulate. Therefore, the composite material can
be handled as a so-called free flowing powder.
[0010] In another particular aspect of the composite material according to the present invention,
the substrate composed of resin is a sheet substrate and the graphene-like carbon
material layer is provided on at least one side of the sheet substrate. In this aspect,
a sheet composite material having excellent adhesion between a carbon material layer
and a sheet substrate can be provided according to the present invention.
[0011] In the composite material according to the present invention, preferably the graphene-like
carbon material is composed of graphene or lamina graphite. Since graphene and lamina
graphite have a high aspect ratio and have a small number of graphene layers, they
can improve physical properties of a composite material when added even in small amounts.
[0012] The method for producing a composite material according to the present invention
is one for producing a composite material configured according to the present invention,
and the method comprises a step of providing a substrate composed of resin and a graphene-like
carbon material and a step of bringing the graphene-like carbon material into contact
with at least part of the surface of the substrate composed of resin and heating under
the action of a supercritical or subcritical fluid.
[0013] In the method according to the present invention, preferably supercritical or subcritical
CO
2 is used as the supercritical or subcritical fluid. CO
2 becomes supercritical at a temperature of about 31.1°C and a pressure of about 7.52
MPa. Therefore CO
2 can swell the surface of the substrate composed of resin in a milder condition compared
to the case of using H
2O or the like. Thus, even when a resin having a low glass transition temperature is
used, the composite material of the present invention can be reliably obtained.
Advantageous Effects of Invention
[0014] In the composite material according to the present invention, graphene-like carbon
is closely attached to a substrate composed of resin, and therefore a composite material
having excellent adhesion between a graphene-like carbon material layer and a substrate
can be prepared.
[0015] Also, in the production method according to the present invention, by heating with
allowing a supercritical or subcritical fluid to act on resin, a graphene-like carbon
material layer is formed on the surface of resin in such a way that graphene-like
carbon is closely attached to the surface of a substrate composed of resin. Thus,
a composite material of the present invention having a graphene-like carbon material
layer which has excellent adhesion to a substrate composed of resin can be prepared.
Also, in the production method of the present invention, since a graphene-like carbon
material layer is formed on the surface of a substrate as described above, the shape
of the substrate is not particularly limited. Therefore, a graphene-like carbon material
layer can be easily formed, according to the present invention, on the surface of
not only a fine particle substrate such as fine resin particles or a sheet substrate,
but also a substrate composed of resin having a complicated shape.
[0016] Further, although fine carbon material particles, i.e., a material to be dispersed,
are highly cohesive and thus have been difficult to homogeneously disperse and attach,
the production method of the present invention easily enables such fine carbon material
particles to be closely attached to the surface of a substrate.
Brief Description of Drawings
[0017]
[Figure 1] Figure 1 is a scanning electron micrograph (75 x) of fine particles prepared
by mixing 1 g of polymethyl methacrylate fine particles and 0.01 g of lamina graphite
and allowing supercritical carbon dioxide (65°C, 35 MPa) to act on the mixture for
5 hours.
[Figure 2] Figure 2 is a scanning electron micrograph (1300 x) of fine particles prepared
by mixing 1 g of polymethyl methacrylate fine particles and 0.01 g of lamina graphite
and allowing supercritical carbon dioxide (65°C, 35 MPa) to act on the mixture for
5 hours.
[Figure 3] Figure 3 is a scanning electron micrograph (550 x) of a cross section of
a fine particle prepared by mixing 1 g of polymethyl methacrylate fine particles and
0.01 g of lamina graphite and allowing supercritical carbon dioxide (65°C, 35 MPa)
to act on the mixture for 5 hours.
[Figure 4] Figure 4 is a scanning electron micrograph (450 x) of fine particles prepared
by mixing 1 g of polymethyl methacrylate fine particles and 0.005 g of lamina graphite
and allowing supercritical carbon dioxide (65°C, 35 MPa) to act on the mixture for
5 hours.
[Figure 5] Figure 5 is a scanning electron micrograph (120 x) of polymethyl methacrylate
fine particles after allowing supercritical carbon dioxide (65°C, 35 MPa) to act on
the fine particles for 5 hours.
[Figure 6] Figure 6 is a scanning electron micrograph (200 x) of fine particles prepared
by mixing 1 g of polystyrene fine particles (Product No. S-20 available from Sekisui
Plastics Co., Ltd.) and 0.01 g of lamina graphite and allowing supercritical carbon
dioxide (55°C, 28 MPa) to act on the mixture for 12 hours.
[Figure 7] Figure 7 is a scanning electron micrograph (500 x) of fine particles prepared
by mixing 1 g of polystyrene fine particles (Product No. S-20 available from Sekisui
Plastics Co., Ltd.) and 0.01 g of lamina graphite and allowing supercritical carbon
dioxide (55°C, 28 MPa) to act on the mixture for 12 hours.
[Figure 8] Figure 8 is a scanning electron micrograph (200 x) of polystyrene fine
particles (Product No. S-20 available from Sekisui Plastics Co., Ltd.) after allowing
supercritical carbon dioxide (55°C, 28 MPa) to act on the fine particles for 5 hours.
[Figure 9] Figure 9 is a scanning electron micrograph (100 x) of fine particles prepared
by mixing 1 g of polystyrene fine particles (Product No. S-30 available from Sekisui
Plastics Co., Ltd.) and 0.001 g of lamina graphite and allowing supercritical carbon
dioxide (60°C, 28 MPa) to act on the mixture for 4.5 hours.
[Figure 10] Figure 10 is a scanning electron micrograph (500 x) of fine particles
prepared by mixing 1 g of polystyrene fine particles (Product No. S-30 available from
Sekisui Plastics Co., Ltd.) and 0.001 g of lamina graphite and allowing supercritical
carbon dioxide (60°C, 28 MPa) to act on the mixture for 4.5 hours.
[Figure 11] Figure 11 is a scanning electron micrograph (100 x) of polystyrene fine
particles (Product No. S-30 available from Sekisui Plastics Co., Ltd.) after allowing
supercritical carbon dioxide (60°C, 28 MPa) to act on the fine particles for 4.5 hours.
[Figure 12] Figure 12 is a scanning electron micrograph (500 x) of polystyrene fine
particles (Product No. S-30 available from Sekisui Plastics Co., Ltd.) after allowing
supercritical carbon dioxide (60°C, 28 MPa) to act on the fine particles for 4.5 hours.
[Figure 13] Figure 13 is a scanning electron micrograph (100 x) of fine particles
prepared by mixing 1 g of polystyrene fine particles (Product No. S-40 available from
Sekisui Plastics Co., Ltd.) and 0.005 g of lamina graphite and allowing supercritical
carbon dioxide (60°C, 28 MPa) to act on the mixture for 4.5 hours.
[Figure 14] Figure 14 is a scanning electron micrograph (100 x) of polystyrene fine
particles (Product No. S-40 available from Sekisui Plastics Co., Ltd.) after allowing
supercritical carbon dioxide (60°C, 28 MPa) to act on the fine particles for 4.5 hours.
[Figure 15] Figure 15 is a scanning electron micrograph (500 x) of fine particles
prepared by mixing 1 g of fine particles of a copolymer of polystyrene and 2-hydroxyethyl
methacrylate (Product No. CS-10 available from Sekisui Plastics Co., Ltd.) and 0.3
g of lamina graphite and allowing supercritical carbon dioxide (35°C, 21 MPa) to act
on the mixture for 12 hours.
[Figure 16] Figure 16 is a scanning electron micrograph (5000 x) of fine particles
prepared by mixing 1 g of fine particles of a copolymer of polystyrene and 2-hydroxyethyl
methacrylate (Product No. CS-10 available from Sekisui Plastics Co., Ltd.) and 0.3
g of lamina graphite and allowing supercritical carbon dioxide (35°C, 21 MPa) to act
on the mixture for 12 hours.
[Figure 17] Figure 17 is a scanning electron micrograph (450 x) of fine particles
of a copolymer of polystyrene and 2-hydroxyethyl methacrylate (Product No. CS-10 available
from Sekisui Plastics Co., Ltd.) after allowing supercritical carbon dioxide (35°C,
21 MPa) to act on the fine particles for 12 hours.
[Figure 18] Figure 18 is a scanning electron micrograph (70 x) of fine particles prepared
by mixing 1 g of fine particles of a copolymer of polystyrene and 2-hydroxyethyl methacrylate
(Product No. CS-50 available from Sekisui Plastics Co., Ltd.) and 0.001 g of lamina
graphite and allowing supercritical carbon dioxide (room temperature, 28 MPa) to act
on the mixture for 12 hours.
[Figure 19] Figure 19 is a scanning electron micrograph (80 x) of fine particles of
a copolymer of polystyrene and 2-hydroxyethyl methacrylate (Product No. CS-50 available
from Sekisui Plastics Co., Ltd.) after allowing supercritical carbon dioxide (room
temperature, 28 MPa) to act on the fine particles for 12 hours.
Description of Embodiments
[0018] Hereinafter specific embodiments of the present invention will be shown in order
to describe the present invention.
(Substrate composed of resin)
[0019] A substrate composed of resin is used for the composite material and the method for
producing the same according to the present invention. As the resin constituting the
substrate, an appropriate resin can be used such that its surface may be softened
by heating under the action of a supercritical or subcritical fluid. The resin may
be synthetic or natural.
[0020] As the above resin, those having a glass transition temperature Tg that causes softening
at a temperature at which a supercritical or subcritical fluid is allowed to act are
preferred. As described later, CO
2 is preferably used as the fluid allowed to act in a supercritical or subcritical
state. Thus resins such as polystyrene, polypropylene, polymethyl methacrylate (PMMA)
and cellulose may be preferably used. The resin may be a copolymer of monomers constituting
such polymers. Of course, as the resin material used in the present invention, various
(meth)acrylic resins in addition to PMMA or various polyolefins in addition to polypropylene
may also be used.
[0021] Even the shape of the above substrate composed of resin is not particularly limited.
The substrate may be fine resin particles. In other words, the substrate may be in
the form of fine particles. The diameter of fine particles is not particularly limited,
and fine particles with an average diameter of 200 µm or less are preferably used.
A substrate composed of resin in the form of particles larger than those may also
be used. When the substrate composed of resin is in the form of particles, the composite
material prepared according to the present invention is less likely to coagulate as
described later. Therefore, the composite material can be handled as a free flowing
powder.
[0022] Alternatively, the substrate composed of resin may be in the form of sheet. In the
case of a sheet substrate, a graphene-like carbon material layer may be formed on
at least part of one side and/or the opposite side of the sheet substrate according
to the present invention.
[0023] Further, the substrate composed of resin used in the present invention may not be
necessarily in the form of particles or sheet. In other words, the substrate composed
of resin may have a complicated three-dimensional shape as long as a graphene-like
carbon material can be brought into contact with at least part of the surface of the
substrate composed of resin and a supercritical or subcritical fluid is allowed to
act thereon in that state. Even in that case, a composite material with a complicated
three-dimensional shape having a graphene-like carbon material layer on the surface
can be prepared according to the present invention.
[0024] Moreover, a graphene-like carbon material may be selectively formed on part of the
complicated surface of the substrate.
(Graphene-like carbon material layer)
[0025] In the composite material according to the present invention, a graphene-like carbon
material layer is provided so as to cover at least part of the surface of the substrate
composed of resin described above. As a graphene-like carbon material constituting
the graphene-like carbon material layer, graphene or lamina graphite may be preferably
used. As is known, graphite is a stack of graphene. Lamina graphite is prepared by
the exfoliation of graphite, and in a lamina graphite stack, the number of graphene
layers is several to about 200. Also, lamina graphite has a specific surface area
of 600 m
2/g or more, which is much greater than that of graphite. In the present invention,
the above lamina graphite is prepared by the exfoliation of graphite, and is a graphene
stack having the number of graphene layers as described above.
[0026] As the above lamina graphite, a commercially available lamina graphite may be used.
Alternatively, various methods of exfoliating graphite may be employed to prepare
lamina graphite.
[0027] The method of preparing lamina graphite described above is not particularly limited,
and lamina graphite may be prepared by the exfoliation of expanded graphite prepared
by expanding graphite. For the process of expanding graphite to prepare expanded graphite,
1) a method of immersing layer graphite in an electrolyte solution and heating, or
2) an electrolysis method may be used.
[0028] The process 1) comprises immersing layer graphite in nitric acid or sulfuric acid
and heating, thereby intercalating nitrate ions or sulfate ions between layers. In
this case, it is desirable that the nitric acid concentration or the sulfuric acid
concentration is about 40% by weight to 70% by weight. A concentration within the
range ensures reliable intercalation of nitrate ions or sulfate ions between layers.
It is preferable that the heating temperature is 20°C or more and 50°C or less. A
temperature within the range ensures reliable intercalation of the nitrate ions or
sulfate ions between layers.
[0029] In the electrolysis process of 2), layer graphite is set at a working electrode,
and the working electrode and a counter electrode composed of Pt or the like are immersed
in nitric acid or sulfuric acid, and electrolysis is carried out. This enables electrolyte
ions such as nitrate ions or sulfate ions to be intercalated between layers of layer
graphite, i.e., between graphenes, and thus the interlayer distance can be increased.
[0030] Next, the sheet of expanded graphite prepared as described above is washed with water
or the like and dried to remove nitrate ions, sulfate ions or the like. A dry sheet
of expanded graphite can be prepared in this way. For preparing lamina graphite by
the exfoliation of expanded graphite, heating or application of ultrasound may be
employed.
[0031] As the graphene-like carbon material in the present invention, not only graphene
or lamina graphite, but also various graphene-like carbon materials which have a graphene
sheet structure on the surface, such as carbon nanotube, may be used.
[0032] In the present invention, the thickness of the above graphene-like carbon material
layer is not particularly limited, and may be properly determined according to the
purpose of use. In the case of providing a graphene-like carbon material layer on
the surface of a substrate composed of fine resin particles, the graphene-like carbon
material layer has a thickness of about 0.5 nm to 500 nm. Likewise, even in the case
of providing a graphene-like carbon material layer on at least one side of a sheet
substrate, the graphene-like carbon material layer may have a thickness of about 0.5
nm to 500 nm.
[0033] When the graphene-like carbon material layer is too thick, the advantageous effect
of resin physical properties may not be obtained. On the other hand, when the graphene-like
carbon material layer is too thin, sufficient effect of improving physical properties
caused by providing the graphene-like carbon material layer may not be obtained.
[0034] In the present invention, some of the graphene-like carbon constituting the above
graphene-like carbon material layer is closely attached to the surface of a substrate.
Preferably some of the graphene-like carbon penetrates the substrate from the surface
of the substrate toward the inner part. This causes an anchor effect that improves
the adhesion between the graphene-like carbon material layer and the substrate composed
of resin effectively.
[0035] The composite material of the present invention in which graphene-like carbon has
excellent adhesion to the surface of a substrate, more preferably the composite material
of the present invention in which some of the graphene-like carbon penetrates the
substrate from the surface of the substrate toward the inner part, can be prepared
by the production method of the present invention.
(Production method)
[0036] In the production method of the present invention, first the above substrate composed
of resin and the above graphene-like carbon material are prepared. Next, the above
graphene-like carbon material is brought into contact with at least part of the surface
of the substrate composed of resin and in that state heating is carried out under
the action of a supercritical or subcritical fluid. CO
2, H
2O or the like may be used as the supercritical or subcritical fluid.
[0037] CO
2 is supercritical at a temperature of 31.1°C and a pressure of about 7.52 MPa. CO
2 is subcritical at -56.6°C to 31.1°C and a pressure ranging from about 0.528 MPa to
7.52 MPa. Heating with allowing a supercritical or subcritical fluid to act thereon
causes softening of the surface of a substrate composed of resin. As a result, graphene-like
carbon comes into contact with the softened surface of the substrate. Preferably,
some of the graphene-like carbon penetrates the surface of the substrate. Thus, when
they are cooled after heating, a graphene-like carbon material layer is formed so
as to cover at least part of the surface of the substrate, with graphene-like carbon
closely attached to the surface of the substrate. Thus, the composite material of
the present invention can be prepared.
[0038] For this reason, it is desirable that the resin constituting the above substrate
composed of resin has a glass transition temperature Tg within the range of temperature
and atmosphere in the process of heating under the action of a supercritical or subcritical
fluid. More specifically, the resin has a glass transition temperature Tg of desirably
in the above heating temperature range of -100°C to +100°C. A glass transition temperature
Tg in this range ensures reliable penetration of some of the graphene-like carbon
into the surface of the substrate composed of resin.
[0039] For bringing a graphene-like carbon material into contact with the surface of the
above substrate composed of resin, the material may be brought into contact with at
least part of the surface of the substrate as described above. The graphene-like carbon
material, however, may also be brought into contact with the entire surface of the
substrate.
[0040] Further, since a graphene-like carbon material is brought into contact with at least
part of the surface of the substrate and heating is carried out in that state under
the action of a supercritical or subcritical fluid as described above, the graphene-like
carbon material can be brought into contact with part of the surface of the substrate
selectively and thus even a composite material in which a graphene-like carbon material
layer is selectively provided on part of the surface of the substrate can be easily
prepared. In addition, as described above, even in the case of using a substrate having
a complicated three-dimensional shape, a graphene-like carbon material layer can be
easily and reliably formed on the surface of the substrate according to the present
invention.
(Physical properties of composite material)
[0041] In the composite material according to the present invention, a graphene-like carbon
material has an improved adhesion to the surface of a substrate as described above,
and preferably a graphene-like carbon material layer is formed in such a manner that
part of the graphene-like carbon material penetrates the surface of the substrate
composed of resin. As a result, the adhesion between the graphene-like carbon material
layer and the substrate can be effectively improved. Therefore, the graphene-like
carbon material layer is less likely to be separated from the substrate even if exposed
to an environment with heat history. Further, due to the excellent adhesion, the carbon
material is effective in improving mechanical strength and the like.
[0042] In addition, the experiments by the present inventors have shown that a composite
material in which the above graphene-like carbon material layer is formed on, for
example, PMMA according to the present invention has a higher glass transition temperature
Tg. Therefore, a composite material having excellent heat resistance can be provided.
It is considered that Tg of the composite material becomes higher as described above
by a stronger interaction between graphene-like carbon and resin caused by the improved
adhesion between the graphene-like carbon material and the surface of PMMA.
[0043] Even in the case of using resin other than PMMA, the Tg of the composite material
can be effectively improved from the Tg of the original resin by forming a graphene-like
carbon material layer according to the present invention. Therefore, a composite material
having excellent heat resistance can be provided.
[0044] Hereinafter Examples and Comparative Examples of the present invention will be described.
The present invention is not limited to the following Examples.
(Example 1)
1) Preparation of lamina graphite
[0045] Product No: PF100-UHP available from Toyo Tanso Co., Ltd. was prepared as a raw material
graphite sheet. A low density graphite sheet with a density of 0.7 and a thickness
of 1 mm was prepared by the same production method as that of the above graphite sheet
at a lower rolling ratio in rolling.
[0046] The graphite sheet with a density of 0.7 prepared as described above was cut into
3 cm x 3 cm to prepare a graphite sheet as an electrode material. Two slits were cut
in the graphite sheet in a length of 1 cm and a width of 1 cm with a cutter knife.
An electrode composed of Pt was inserted into the graphite sheet in which two slits
were formed. The graphite sheet prepared as described above which was employed as
a working electrode (anode), a counter electrode (cathode) composed of Pt and a reference
electrode composed of Ag/AgCl were immersed in an aqueous nitric acid solution at
a concentration of 60% by weight and a DC voltage was applied thereto to carry out
an electrochemical treatment. In this way, the graphite used at the anode as a working
electrode was formed into expanded graphite.
[0047] Next, the resulting expanded graphite was dried and cut into 1 cm square pieces and
one of them was put in a carbon crucible to be subjected to electromagnetic induction
heating. This was carried out by using induction heating equipment MU 1700D made by
SK MEDICAL ELECTRONICS CO., LTD. in argon gas atmosphere with the highest temperature
reached of 550°C at a current amount of 10 A. The expanded graphite was exfoliated
by the electromagnetic induction heating. The specific surface area of the resulting
lamina graphite powder was measured by using specific surface area analyzer ASAP-2000
made by Shimadzu Corporation with nitrogen gas and as a result, the specific surface
area was 850 m
2/g in a single measurement.
2) Production of composite material
[0048] Fine particles of polymethyl methacrylate (available from Sigma-Aldrich Co., LLC.,
Product No.: 445746-500G, Mw: 350,000, Tg: 122°C) were prepared as a substrate composed
of resin. 1.0 g of the polymethyl methacrylate fine particles and 0.01 g of lamina
graphite prepared as described above were put in a pressure vessel. 10 mL of CO
2 which is supercritical at room temperature (23°C) and a pressure of 10 MPa was added
thereto, and then CO
2 was once removed (for drying by removing water). Thereafter 10 mL of CO
2 which is supercritical at room temperature (23°C) and a pressure of 10 MPa was added
thereto again. Subsequently the temperature was increased to 65°C and the mixture
was heated for 5 hours with stirring. The pressure increased to about 35 MPa at this
stage. Then the resultant was cooled to room temperature to prepare a composite material.
The resulting composite material was in the form of particles and had an average particle
size of 120 µm. Also, the surface of the composite material particles prepared as
described above was observed by a scanning electron microscope (JCM-5700 made by JEOL
Ltd.).
[0049] Figure 1 is a scanning electron micrograph of the composite material particles prepared
in Example 1 magnified 75 times; and Figure 2 is a scanning electron micrograph of
the surface of the particles enlarged 1300 times.
[0050] Some of the above particles were broken by using a mortar and the broken particles
were also observed by the scanning electron microscope (JCM-5700 made by JEOL Ltd.).
Figure 3 is a scanning electron micrograph magnified 550 times taken as described
above. As can be seen from Figure 1 to Figure 3, in the resulting composite material,
a graphene-like carbon material is formed on the surface of fine particles. In particular,
the micrograph of Figure 3 shows that graphene-like carbon is accumulated on the surface
of substrate particles.
(Example 2)
[0051] 0.005 g of the same lamina graphite as that in Example 1 and 1.0 g of fine particles
of polymethyl methacrylate (available from Sigma-Aldrich Co., LLC., Product No: 445746-500G,
Mw: 350,000, Tg: 122°C) were mixed and put in a pressure vessel as in Example 1. 10
mL of CO
2 which is supercritical at room temperature (23°C) and a pressure of 10 MPa was added
thereto, and then CO
2 was once removed (for drying by removing water). Thereafter 10 mL of CO
2 which is supercritical at room temperature (23°C) and a pressure of 10 MPa was added
thereto again. Subsequently the temperature was increased to 65°C and the mixture
was heated for 5 hours with stirring. The pressure increased to about 35 MPa at this
stage. Then the resultant was cooled to room temperature to prepare a composite material.
The resulting composite material was in the form of particles and had an average particle
size of 120 µm. Also, the surface of the composite material particles prepared as
described above was observed by a scanning electron microscope (JCM-5700 made by JEOL
Ltd.).
[0052] Figure 4 is a scanning electron micrograph of the composite material particles prepared
in Example 2 magnified 450 times. The micrograph of Figure 4 shows that some of the
graphene-like carbon has penetrated the surface of the original substrate particles
composed of resin.
(Comparative Example 1)
[0053] For Comparative Example, polymethyl methacrylate fine particles which were the material
in Example were prepared. Figure 5 shows a scanning electron micrograph of the polymethyl
methacrylate fine particles magnified 120 times. As can be seen from Figure 5, no
graphene-like carbon is present on the surface of the polymethyl methacrylate fine
particles and therefore the particles have a smooth surface.
(Example 3)
[0054] 0.01 g of the same lamina graphite as that in Example 1 and 1.0 g of fine particles
of polystyrene (available from Sekisui Plastics Co., Ltd., Product No: S-20, average
particle size: 300 µm, Tg: 106°C) were mixed and put in a pressure vessel as in Example
1. 10 mL of CO
2 which is supercritical at room temperature (23°C) and a pressure of 10 MPa was added
thereto, and then CO
2 was once removed (for drying by removing water). Thereafter 10 mL of CO
2 which is supercritical at room temperature (23°C) and a pressure of 10 MPa was added
thereto again. Subsequently the temperature was increased to 55°C and the mixture
was heated for 12 hours with stirring. The pressure increased to about 28 MPa at this
stage. Then the resultant was cooled to room temperature to prepare a composite material.
The surface of the composite material particles prepared was observed by a scanning
electron microscope (JCM-5700 made by JEOL Ltd.).
[0055] Figure 6 and Figure 7 are a scanning electron micrograph of the composite material
particles prepared in Example 3 magnified 200 and 500 times, respectively. The micrographs
of Figure 6 and Figure 7 show that some of the graphene-like carbon has penetrated
the surface of the original substrate particles composed of resin.
(Comparative Example 2)
[0056] Polystyrene fine particles which were the material in Example 3 were prepared. Figure
8 shows a scanning electron micrograph of the polystyrene fine particles magnified
200 times. As can be seen from Figure 8, no graphene-like carbon is present on the
surface of the polystyrene fine particles and therefore the particles have a smooth
surface.
(Example 4)
[0057] A composite material was prepared in the same manner as in Example 3 except for mixing
0.001 g of the same lamina graphite as that in Example 1 and 1.0 g of fine particles
of polystyrene (available from Sekisui Plastics Co., Ltd., Product No: S-30, average
particle size: 800 µm, Tg: 105°C), increasing the temperature to 60°C and heating
for 4.5 hours with stirring. The pressure increased to 28 MPa at the time of mixing.
The surface of the composite material particles prepared was observed by a scanning
electron microscope (JCM-5700 made by JEOL Ltd.).
[0058] Figure 9 and Figure 10 are a scanning electron micrograph of the composite material
particles prepared in Example 4 magnified 100 and 500 times, respectively. The micrograph
of Figure 5 shows that some of the graphene-like carbon has penetrated the surface
of the original substrate particles composed of resin.
(Comparative Example 3)
[0059] Polystyrene fine particles which were the material in Example 4 were prepared. Figure
11 and Figure 12 show a scanning electron micrograph of the polystyrene fine particles
magnified 100 and 500 times, respectively. As can be seen from Figure 11 and Figure
12, no graphene-like carbon is present on the surface of the polymethyl methacrylate
fine particles and therefore the particles have a smooth surface.
(Example 5)
[0060] A composite material was prepared in the same manner as in Example 4 except for mixing
0.005 g of the same lamina graphite as that in Example 1 and 1.0 g of fine particles
of polystyrene (available from Sekisui Plastics Co., Ltd., Product No: S-40, average
particle size: 600 µm, Tg: 105°C). The pressure increased to about 28 MPa at the time
of mixing. The surface of the composite material particles prepared was observed by
a scanning electron microscope (JCM-5700 made by JEOL Ltd.).
[0061] Figure 13 is a scanning electron micrograph of the composite material particles prepared
in Example 5 magnified 100 times. The micrograph of Figure 13 shows that some of the
graphene-like carbon has penetrated the surface of the original substrate particles
composed of resin.
(Comparative Example 4)
[0062] Polystyrene fine particles which were the material in Example 5 were prepared. Figure
14 shows a scanning electron micrograph of the polystyrene fine particles magnified
100 times. As can be seen from Figure 14, no graphene-like carbon is present on the
surface of the fine particles and therefore the particles have a smooth surface.
(Example 6)
[0063] A composite material was prepared in the same manner as in Example 3 except for mixing
0.3 g of the same lamina graphite as that in Example 1 and 1.0 g of fine particles
of a copolymer of polystyrene and 2-hydroxyethyl methacrylate (available from Sekisui
Plastics Co., Ltd., Product No: CS-10, average particle size: 100 µm, Tg: 98°C), increasing
the temperature to 35°C and stirring for 12 hours. The pressure increased to about
21 MPa at the time of mixing. The surface of the composite material particles prepared
was observed by a scanning electron microscope (JCM-5700 made by JEOL Ltd.).
[0064] Figure 15 and Figure 16 are a scanning electron micrograph of the composite material
particles prepared in Example 6 magnified 500 and 5000 times, respectively. The micrographs
of Figure 15 and Figure 16 show that some of the graphene-like carbon has penetrated
the surface of the original substrate particles composed of resin.
(Comparative Example 5)
[0065] Fine particles of a copolymer of polystyrene and 2-hydroxyethyl methacrylate which
were the material in Example 6 were prepared. Figure 17 shows a scanning electron
micrograph of the fine particles magnified 450 times. As can be seen from Figure 17,
no graphene-like carbon is present on the surface of the fine particles and therefore
the particles have a smooth surface.
(Example 7)
[0066] A composite material was prepared in the same manner as in Example 3 except for mixing
0.001 g of the same lamina graphite as that in Example 1 and 1.0 g of fine particles
of a copolymer of polystyrene and butyl acrylate (available from Sekisui Plastics
Co., Ltd., Product No: CS-50, average particle size: 1100 µm, Tg: 46°C) and stirring
with maintaining the temperature at room temperature for 12 hours. The pressure increased
to about 28 MPa at the time of mixing. The surface of the composite material particles
prepared was observed by a scanning electron microscope (JCM-5700 made by JEOL Ltd.).
[0067] Figure 18 is a scanning electron micrograph of the composite material particles prepared
in Example 7 magnified 70 times. The micrograph of Figure 18 shows that some of the
graphene-like carbon has penetrated the surface of the original substrate particles
composed of resin.
(Comparative Example 6)
[0068] Fine particles of a copolymer of styrene and butyl acrylate which were the material
in Example 7 were prepared. Figure 19 shows a scanning electron micrograph of the
fine particles magnified 80 times. As can be seen from Figure 19, no graphene-like
carbon is present on the surface of the fine particles and therefore the particles
have a smooth surface.